Zinc-cobalt Double Metal Cyanide Complex Research Articles

Synthesis of high-molecular-weight poly(ε-caprolactone) via heterogeneous zinc-cobalt(III) double metal cyanide complex

The synthesis of high-molecular-weight poly(ε-caprolactone)s (PCLs) with enhanced mechanical properties remains challenging. Here we demonstrate the heterogeneous catalysis for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). Using a zinc-cobalt double-metal cyanide complex [Zn-Co(III) DMCC] in the presence of around 1% mol epoxides, PCLs are achieved with high number-average molecular weights (Mns) of up to 177.7 kDa determined by the gel permeation chromatography. The [Zn]-OH active site of the complex triggers the cleavage of the epoxide at first, which is considered as the rate-determining step of the polymerization. The formed zinc-alkoxide species then initiates the ROP of ε-CL, affording most of the PCLs possessing one epoxide molecule embedded in the polymer chain and dihydroxyl terminals as revealed by the 1H NMR and MALDI-TOF MS spectroscopy. The PCL specimen with a corrected Mn of 110.4 kDa exhibits the tensile strength and elongation at break of as high as 40.2 MPa and 1060%, respectively. This work provides a facile and practical method for the synthesis of high-molecular-weight PCLs.

Poly(monothiocarbonate)s from the Alternating and Regioselective Copolymerization of Carbonyl Sulfide with Epoxides.

Carbonyl sulfide (COS) is an air pollutant that causes acid rain, ozonosphere damage, and carbon dioxide (CO2) generation. It is a heterocumulene and structural analogue of CO2. Relevant to organic synthesis, it is a source of C═O or C═S groups and thus an ideal one-carbon (C1) building block for synthesizing sulfur-containing polymers through the similar route of CO2 copolymerization. In contrast, traditional synthesis of sulfur-containing polymers often involves the condensation of thiols with phosgene and ring-opening polymerization of cyclic thiocarbonates that are generally derived from thiols and phosgene; thus, COS/epoxide copolymerization is a "greener" route to supplement or supplant current processes for the production of sulfur-containing polymers. This Accounts highlights our efforts on the discovery of the selective formation of poly(monothiocarbonate)s from COS with epoxides via heterogeneous zinc-cobalt double metal cyanide complex (Zn-Co(III) DMCC) and homogeneous (salen)CrX complexes. The catalytic activity and selectivity of Zn-Co(III) DMCC for COS/epoxide copolymerization are similar to those for CO2/epoxide copolymerization. (salen)CrX complexes accompanied by onium salts exhibited high activity and selectivity for COS/epoxide copolymerization under mild conditions, affording copolymers with >99% monothiocarbonate units and high tail-to-head content up to 99%. By way of contrast, these catalysts often show moderate or low activity for CO2/epoxide copolymerization. Of note, a specialty of COS/epoxide copolymerization is the occurrence of an oxygen-sulfur exchange reaction (O/S ER), which may produce carbonate and dithiocarbonate units. O/S ER, which are induced by the metal-OH bond regenerated by chain transfer reactions, can be kinetically inhibited by changing the reaction conditions. We provide a thorough mechanistic understanding of the electronic/steric effect of the catalysts on the regioselectivity of COS copolymerization. The regioselectivity of the copolymerization originates from the solely nucleophilic attack of the sulfur anion to methylene of the epoxide, and thus, the chiral configuration of the monosubstituted epoxides is retained. COS-based copolymers are highly transparent sulfur-containing polymers with excellent optical properties, such as high refractive index and Abbe number. Thanks to their good solubility and many available epoxides, COS/epoxide copolymers can potentially be a new applicable optical material. Very recently, crystalline COS-based polymers with or without chiral carbons have been synthesized, which may further expand the scope of application of these new materials.

Highly efficient one-pot/one-step synthesis of multiblock copolymers from three-component polymerization of carbon dioxide, epoxide and lactone.

It is a long-standing challenge to combine mixed monomers into multiblock copolymer (MBC) in a one-pot/one-step polymerization manner. We report the first example of MBC with biodegradable polycarbonate and polyester blocks that were synthesized from highly efficient one-pot/one-step polymerization of cyclohexene oxide (CHO), CO2 and ε-caprolactone (ε-CL) in the presence of zinc-cobalt double metal cyanide complex and stannous octoate. In this protocol, two cross-chain exchange reactions (CCER) occurred at dual catalysts respectively and connected two independent chain propagation procedures (i.e., polycarbonate formation and polyester formation) simultaneously in a block-by-block manner, affording MBC without tapering structure. The multiblock structure of MBC was determined by the rate ratio of CCER to the two chain propagations and could be simply tuned by various kinetic factors. This protocol is also of significance due to partial utilization of renewable CO2 and improved mechanical properties of the resultant MBC.

Alternating copolymerization of carbonyl sulfide and Cyclohexene Oxide catalyzed by zinc–cobalt double metal cyanide complex

This paper describes the first example of alternating copolymerization of carbonyl sulfide (COS) with cyclohexene oxide (CHO) via heterogenous catalysis of a nano-lamellar zinc–cobalt(III) double metal cyanide complex (Zn–Co(III) DMCC), providing an efficient method for converting COS to poly(cyclohexene monothiocarbonate) (PCHMTC) with an alternating degree up to 93%. The number-average molecular weight (Mn) of PCHMTC was 6.5–25.0 kg/mol with polydispersities (PDIs) of 1.6–2.1. The productivity of the catalyst was up to 970 g polymer/g catalyst (5.0 h). The oxygen–sulfur exchange reaction (O/S ER) caused by Zn–Co(III) DMCC was largely suppressed when the reaction was performed at 100–110 °C in the presence of THF or CH2Cl2, and thus the selectivity of the monothiocarbonate over carbonate linkages was up to 98%. The mechanisms of the copolymerization and O/S ER were proposed based on the ESI-MS, GC–MS and FT-IR spectra. The obtained PCHMTC is highly transparent and exhibits good solubility in various organic solvents, high Tg of 112 °C, initial decomposition temperature of 214 °C and high refractive index of 1.705.

Functional poly(carbonate-co-ether) synthesis from glycidyl methacrylate/CO2copolymerization catalyzed by Zn–Co(iii) double metal cyanide complex catalyst

Polycarbonates with pendant functional groups have attracted much attention due to their capability for further chemical modification and post-polymerization. This work describes the synthesis of a poly(carbonate-co-ether) with massive pendant acrylate groups from the copolymerization of glycidyl methacrylate (GMA) with carbon dioxide (CO2), using a nanolamellar zinc-cobalt double metal cyanide complex (Zn–Co(III) DMCC) catalyst. The carbonate linkage content (FCO2) of the poly(carbonate-co-ether) could be varied from 42.2 to 68.0% by changing the polymerization conditions. Of importance, 4-methoxyphenol was applied for regulating the copolymerization. It could not only act as an inhibitor for completely depressing the self-polymerization of GMA via free radical polymerization of the double bond, but also modulate the molecular weight of the resultant copolymers. The obtained copolymer had two terminal hydroxyl groups, which were confirmed by the electrospray ionization-tandem mass spectrometry (ESI-MS) technique. A new thermoset with high glass transition temperature (Tg: 105 or 120 °C) and massive carbonate units as well as hydroxyl (or carboxylic) groups was prepared by the curing reaction of the GMA–CO2 copolymer with allyl alcohol or acrylic acid in the presence of 2,2′-azobisisobutyronitrile (AIBN).

Selective production of poly(carbonate–co–ether) over cyclic carbonate for epichlorohydrin and CO2 copolymerization via heterogeneous catalysis of Zn–Co (III) double metal cyanide complex

Epichlorohydrin (ECH), as a cheap raw chemical material, is an ideal monomer for copolymerization with CO2 to produce biodegradable polycarbonates. This work describes the selective ECH–CO2 copolymerization via heterogeneous catalysis of nanolamellar zinc–cobalt double metal cyanide complex (Zn–Co (III) DMCC), affording a poly(carbonate–co–ether) with carbonate content up to 70.7%. Remarkably, the cyclic carbonate contents in the product are 5.0%–11.3% at 25–60 °C, better than those from homogeneous catalysis. Moreover, the copolymer with 70.7% carbonate content presents high thermal decomposition temperature of 250 °C and relatively high glass-transition temperature (Tg) of 31.2 °C.

Highly active and selective binary catalyst system for the coupling reaction of CO2 and hydrous epoxides

Although most of the zinc-containing catalysts show excellent catalytic activity for the coupling reaction of carbon dioxide (CO2) with epoxides, generally, trace amounts of water in the reaction systems could cause a significant decrease of the catalytic activity. In this work, a nanoporous zinc-cobalt double metal cyanide complex (Zn–CoIII DMCC) with high surface area was synthesized via a modified hydrothermal process using tri-block copolymer EO20PO70EO20 (P123) as the template. When cetyltrimethylammonium bromide (CTAB) was used as the co-catalyst, the Zn–CoIII DMCC/CTAB binary catalyst system could effectively catalyze the coupling reaction of CO2 with hydrous propylene oxide (PO), producing propylene carbonate (PC) with nearly 100% productivity and 100% selectivity. This binary catalyst system could also catalyze the coupling reaction of other commercial epoxides and CO2 without using any solvents with nearly 100% productivity and 100% selectivity. With such new catalyst system, hundreds of ppm water in the reaction system will no longer be the matter.

Synthesis of bis(cyclic carbonate) and propylene carbonate via a one-pot coupling reaction of CO2, bisepoxide and propylene oxide

The effective transformation of carbon dioxide (CO2) into valuable products is promising in green and sustainable chemistry. The coupling reaction of CO2 with epoxides to afford cyclic carbonates is an atom-economic pathway for CO2 fixation. Many catalysts have been developed for this coupling reaction, however, very few of them were reported for the coupling reaction of CO2 with bisepoxides. This work describes an efficient one-pot coupling reaction of CO2, propylene oxide (PO) and bisepoxides without the addition of external organic solvents by using a nanolamellar zinc-cobalt double metal cyanide complex (Zn–Co(III) DMCC) as the catalyst and cetyltrimethyl-ammonium bromide (CTAB) as the co-catalyst. Propylene carbonate (PC) and bis(cyclic carbonate)s were obtained at the same time with high monomer conversions (PO: 93.6%, bisepoxides: 82.9%). The in situ produced PC acted as a good solvent for the coupling reaction of CO2 with bisepoxides. Two products could be easily separated by distillation or precipitation. The application of the obtained bis(cyclic carbonate)s was also preliminarily investigated. A non-isocyanate route for synthesizing polyurethanes with massive hydroxyl groups was proposed.

Dicarboxylic acid promoted immortal copolymerization for controllable synthesis of low‐molecular weight oligo(carbonate‐ether) diols with tunable carbonate unit content

AbstractLow‐molecular weight oligo(carbonate‐ether) diols are important raw materials for polyurethane formation, which with tunable carbonate unit content (CU) may endow new thermal and mechanical performances to polyurethane. Herein, facile synthesis of oligo(carbonate‐ether) diols with number average molecular weight (Mn) below 2000 g mol−1 and CU tunable between 40% and 75% are realized in high activity by immortal copolymerization of CO2/propylene oxide (PO) using zinc‐cobalt double metal cyanide complex (Zn‐Co‐DMCC) in the presence of sebacic acid (SA). Mn of the oligomer is in good linear relationship to the mole ratio of PO and SA (PO/SA) and hence can be precisely controlled by adjusting PO/SA. Besides, the molecular weight distribution is quite narrow due to the rapid reversible chain transfer in the immortal copolymerization. High pressure and low temperature are favorable for raising CU. In all the reactions, the weight fraction of propylene carbonate (WPC) can even be controlled as low as 2.0 wt %, and the catalytic activity of Zn‐Co‐DMCC is above 1.0 kgg−1 cat. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Selective synthesis of oligo(carbonate-ether) diols from copolymerization of CO2 and propylene oxide under zinc-cobalt double metal cyanide complex

Colorless oligo(carbonate-ether) diols were selectively synthesized in high efficiency from copolymerization of CO2 and propylene oxide (PO) using Zn3[Co(CN)6]2-based double metal cyanide complex (DMC) as catalyst and different molecular weight polypropylene glycols (PPGs) as chain transfer agent. The catalytic activity was related to carbonate unit content and molecular weight of target oligo(carbonate-ether) diols, for oligo(carbonate-ether) diol with number average molecular weight of 6.4 kg/mol and carbonate unit content of 34.3 %, it reached 10.0 kg oligomer/g DMC catalyst during 10 h of copolymerization. Generally, the number average molecular weight of the oligo(carbonate-ether) diol was tunable between 1.8 kg/mol and 6.4 kg/mol, and the molecular weight distribution was controllable between 1.14 and 1.83. Moreover, the carbonate unit content in the oligo-diols can be adjusted between 15.3 % and 62.5 %, lower temperature and higher CO2 pressure were favorable for higher carbonate content. Better selectivity of oligo(carbonate-ether)diol over propylene carbonate(PC) was realized, where the weight ratio of PC (WPC) was controlled less than 8.0 wt%. We also found that the alkali metal ion residue may play an important role in PC formation, in some cases this effect may be more significant than backbiting process, removing the residual alkali metal ion should be meaningful in the future to further reduce the PC formation.

Chromosome investigations of persons exposed to dimethylcarbamoyl chloride and diethylcarbamoyl chloride

Although most of the zinc-containing catalysts show excellent catalytic activity for the coupling reaction of carbon dioxide (CO2) with epoxides, generally, trace amounts of water in the reaction systems could cause a significant decrease of the catalytic activity. In this work, a nanoporous zinc-cobalt double metal cyanide complex (Zn–CoIII DMCC) with high surface area was synthesized via a modified hydrothermal process using tri-block copolymer EO20PO70EO20 (P123) as the template. When cetyltrimethylammonium bromide (CTAB) was used as the co-catalyst, the Zn–CoIII DMCC/CTAB binary catalyst system could effectively catalyze the coupling reaction of CO2 with hydrous propylene oxide (PO), producing propylene carbonate (PC) with nearly 100% productivity and 100% selectivity. This binary catalyst system could also catalyze the coupling reaction of other commercial epoxides and CO2 without using any solvents with nearly 100% productivity and 100% selectivity. With such new catalyst system, hundreds of ppm water in the reaction system will no longer be the matter.